Rock cutting and excavation machines have been developed for various specific applications including mining, trenching, tunnelling, foundation drilling, road milling, etc. Typically, a drive body in the form of a rotatable drum or drill head comprises a plurality of replaceable cutting bits that provide the points of contact for the material or mineral face.
For example, a mobile mining machine includes a rotatable cutting head with the cutting bits provided on rotating drums. As the bits contact the surface of the seam they occasionally break and inevitably wear resulting in decreased cutting inefficiency and a need for replacement. It is therefore desirable to mount the cutting bits at the cutting head (or drive body) via releasable mounting assemblies that enable the bits to be replaced conveniently and quickly during servicing and repair.
Cutting bit (alternatively termed ‘cutting pick’ or ‘tool pick’) mountings are described in U.S. Pat. Nos. 3,342,531; 3,627,381; 3,932,952; 4,343,516; 5,261,499; WO 96/31682; US 2008/0258536; US 2008/0309148; WO 2010/027315; US 2011/0278908 and EP 2514918.
Cutting bits have been developed that may be considered to fall in at least two general categories. A first general type comprises a nose portion attached at one end of an elongate shaft whilst a second type comprises a bit head having an inner cavity that fits onto an end of an ‘adaptor’ that comprises a projection head and an elongate shaft, with the head received within the inner cavity of the bit and the shank secured at a through bore extending within a mount body.
A requirement of projection mounted cutting bits of the type described in EP 2514918 is that the bit is capable of unhindered rotation about the projection during cutting. Additionally, the recess region of the bit and parts of the projection must mate cooperatively so as to effectively transfer the significant compressive forces encountered during use. Due to the harsh working environment of the cutting bits, it is common for dust particles and the like to be entrained into the region of the bit recess causing hindered rotation of the bit head and accordingly premature wear that in turn significantly lowers the operational lifetime of the bit and can damage the bit holder. There is therefore a need for a cutting bit and mounting assembly that addresses these problems.